html,body,div,ul,ol,li,dl,dt,dd,h1,h2,h3,h4,h5,h6,pre,form,p,blockquote,fieldset,input
{
    margin: 0;
    padding: 0;
}

body {
    width:100%;
    height:100%;
}
.mainContainer{
    width:630px;
    height:100%;
    margin-left:auto;
    margin-right:auto;
}

#div1{
    float:left;
    width:210px;
    height:100%;
    background:yellow;
}
#div2{
    float:right;
    width:210px;
    height:100%;
    background:green;
}
#div3{
    float:right;
    width:210px;
    height:100%;
    background:red;
}
#div4{
    width:560px;
    height:40px;
    position:absolute;
    background:brown;
    margin-left:auto;
    margin-right:auto;
    margin:40px;

}